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Code Issues Releases Wiki Activity

Stop providing branch prediction information

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The __builtin_expect() can be used to provide the compiler with branch
prediction information.  The Gcc manual says[1] on the subject:

    In general, you should prefer to use actual profile feedback for
    this (-fprofile-arcs), as programmers are notoriously bad at
    predicting how their programs actually perform.

Stop using __builtin_expect() and ISC_LIKELY() and ISC_UNLIKELY() macros
to provide the branch prediction information as the performance testing
shows that named performs better when the __builtin_expect() is not
being used.

1. https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fexpect
This commit is contained in:
Ondřej Surý
2021-10-14 10:33:24 +02:00
parent 80fedf9231
commit e603983ec9
25 changed files with 114 additions and 180 deletions
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33
lib/isc/mem.c
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@@ -187,9 +187,8 @@ struct isc_mempool {
#else /* if !ISC_MEM_TRACKLINES */
#define TRACE_OR_RECORD (ISC_MEM_DEBUGTRACE | ISC_MEM_DEBUGRECORD)
#define SHOULD_TRACE_OR_RECORD(ptr) \
(ISC_UNLIKELY((isc_mem_debugging & TRACE_OR_RECORD) != 0) && \
ptr != NULL)
#define SHOULD_TRACE_OR_RECORD(ptr) \
((isc_mem_debugging & TRACE_OR_RECORD) != 0 && ptr != NULL)
#define ADD_TRACE(a, b, c, d, e) \
if (SHOULD_TRACE_OR_RECORD(b)) { \
@@ -303,8 +302,8 @@ delete_trace_entry(isc_mem_t *mctx, const void *ptr, size_t size,
idx = hash % DEBUG_TABLE_COUNT;
dl = ISC_LIST_HEAD(mctx->debuglist[idx]);
while (ISC_LIKELY(dl != NULL)) {
if (ISC_UNLIKELY(dl->ptr == ptr)) {
while (dl != NULL) {
if (dl->ptr == ptr) {
ISC_LIST_UNLINK(mctx->debuglist[idx], dl, link);
decrement_malloced(mctx, sizeof(*dl));
sdallocx(dl, sizeof(*dl), 0);
@@ -325,7 +324,7 @@ unlock:
#endif /* ISC_MEM_TRACKLINES */
#define ADJUST_ZERO_ALLOCATION_SIZE(s) \
if (ISC_UNLIKELY(s == 0)) { \
if (s == 0) { \
s = ZERO_ALLOCATION_SIZE; \
}
@@ -341,7 +340,7 @@ mem_get(isc_mem_t *ctx, size_t size) {
ret = mallocx(size, 0);
INSIST(ret != NULL);
if (ISC_UNLIKELY((ctx->flags & ISC_MEMFLAG_FILL) != 0)) {
if ((ctx->flags & ISC_MEMFLAG_FILL) != 0) {
memset(ret, 0xbe, size); /* Mnemonic for "beef". */
}
@@ -356,7 +355,7 @@ static inline void
mem_put(isc_mem_t *ctx, void *mem, size_t size) {
ADJUST_ZERO_ALLOCATION_SIZE(size);
if (ISC_UNLIKELY((ctx->flags & ISC_MEMFLAG_FILL) != 0)) {
if ((ctx->flags & ISC_MEMFLAG_FILL) != 0) {
memset(mem, 0xde, size); /* Mnemonic for "dead". */
}
sdallocx(mem, size, 0);
@@ -371,7 +370,7 @@ mem_realloc(isc_mem_t *ctx, void *old_ptr, size_t old_size, size_t new_size) {
new_ptr = rallocx(old_ptr, new_size, 0);
INSIST(new_ptr != NULL);
if (ISC_UNLIKELY((ctx->flags & ISC_MEMFLAG_FILL) != 0)) {
if ((ctx->flags & ISC_MEMFLAG_FILL) != 0) {
ssize_t diff_size = new_size - old_size;
void *diff_ptr = (uint8_t *)new_ptr + old_size;
if (diff_size > 0) {
@@ -483,7 +482,7 @@ mem_create(isc_mem_t **ctxp, unsigned int flags) {
ISC_LIST_INIT(ctx->pools);
#if ISC_MEM_TRACKLINES
if (ISC_UNLIKELY((isc_mem_debugging & ISC_MEM_DEBUGRECORD) != 0)) {
if ((isc_mem_debugging & ISC_MEM_DEBUGRECORD) != 0) {
unsigned int i;
ctx->debuglist =
@@ -524,7 +523,7 @@ destroy(isc_mem_t *ctx) {
INSIST(ISC_LIST_EMPTY(ctx->pools));
#if ISC_MEM_TRACKLINES
if (ISC_UNLIKELY(ctx->debuglist != NULL)) {
if (ctx->debuglist != NULL) {
debuglink_t *dl;
for (i = 0; i < DEBUG_TABLE_COUNT; i++) {
for (dl = ISC_LIST_HEAD(ctx->debuglist[i]); dl != NULL;
@@ -903,10 +902,10 @@ isc__mem_reget(isc_mem_t *ctx, void *old_ptr, size_t old_size,
size_t new_size FLARG) {
void *new_ptr = NULL;
if (ISC_UNLIKELY(old_ptr == NULL)) {
if (old_ptr == NULL) {
REQUIRE(old_size == 0);
new_ptr = isc__mem_get(ctx, new_size FLARG_PASS);
} else if (ISC_UNLIKELY(new_size == 0)) {
} else if (new_size == 0) {
isc__mem_put(ctx, old_ptr, old_size FLARG_PASS);
} else {
DELETE_TRACE(ctx, old_ptr, old_size, file, line);
@@ -935,9 +934,9 @@ isc__mem_reallocate(isc_mem_t *ctx, void *old_ptr, size_t new_size FLARG) {
REQUIRE(VALID_CONTEXT(ctx));
if (ISC_UNLIKELY(old_ptr == NULL)) {
if (old_ptr == NULL) {
new_ptr = isc__mem_allocate(ctx, new_size FLARG_PASS);
} else if (ISC_UNLIKELY(new_size == 0)) {
} else if (new_size == 0) {
isc__mem_free(ctx, old_ptr FLARG_PASS);
} else {
size_t old_size = sallocx(old_ptr, 0);
@@ -1289,7 +1288,7 @@ isc__mempool_get(isc_mempool_t *restrict mpctx FLARG) {
mpctx->allocated++;
if (ISC_UNLIKELY(mpctx->items == NULL)) {
if (mpctx->items == NULL) {
isc_mem_t *mctx = mpctx->mctx;
const size_t fillcount = mpctx->fillcount;
/*
@@ -1442,7 +1441,7 @@ isc__mem_checkdestroyed(void) {
LOCK(&contextslock);
if (!ISC_LIST_EMPTY(contexts)) {
#if ISC_MEM_TRACKLINES
if (ISC_UNLIKELY((isc_mem_debugging & TRACE_OR_RECORD) != 0)) {
if ((isc_mem_debugging & TRACE_OR_RECORD) != 0) {
print_contexts(file);
}
#endif /* if ISC_MEM_TRACKLINES */